48,773 research outputs found

    Simplified dark matter models in the light of AMS-02 antiproton data

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    In this work we perform an analysis of the recent AMS-02 antiproton flux and the antiproton-to-proton ratio in the framework of simplified dark matter models. To predict the AMS-02 observables we adopt the propagation and injection parameters determined by the observed fluxes of nuclei. We assume that the dark matter particle is a Dirac fermionic dark matter, with leptophobic pseudoscalar or axialvector mediator that couples only to Standard Model quarks and dark matter particles. We find that the AMS-02 observations are consistent with the dark matter hypothesis within the uncertainties. The antiproton data prefer a dark matter (mediator) mass in the 700 GeV--5 TeV region for the annihilation with pseudoscalar mediator and greater than 700 GeV (200 GeV--1 TeV) for the annihilation with axialvector mediator, respectively, at about 68% confidence level. The AMS-02 data require an effective dark matter annihilation cross section in the region of 1x10^{-25} -- 1x10^{-24} (1x10^{-25} -- 4x10^{-24}) cm^3/s for the simplified model with pseudoscalar (axialvector) mediator. The constraints from the LHC and Fermi-LAT are also discussed.Comment: 16 pages, 6 figures, 1 table. arXiv admin note: text overlap with arXiv:1509.0221

    Decoupling MSSM Higgs Sector and Heavy Higgs Decay

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    The decoupling limit in the MSSM Higgs sector is the most likely scenario in light of the Higgs discovery. This scenario is further constrained by MSSM Higgs search bounds and flavor observables. We perform a comprehensive scan of MSSM parameters and update the constraints on the decoupling MSSM Higgs sector in terms of 8 TeV LHC data. We highlight the effect of light SUSY spectrum in the heavy neutral Higgs decay in the decoupling limit. We find that the chargino and neutralino decay mode can reach at most 40% and 20% branching ratio, respectively. In particular, the invisible decay mode BR(H^0(A^0) -> \tilde{\chi}^0_1\tilde{\chi}^0_1) increases with increasing Bino LSP mass and is between 10%-15% (20%) for 30<m_{\tilde{\chi}^0_1}<100 GeV. The leading branching fraction of heavy Higgses decay into sfermions can be as large as 80% for H^0 -> \tilde{t}_1\tilde{t}_1^\ast and 60% for H^0/A^0 -> \tilde{\tau}_1\tilde{\tau}_2^\ast+\tilde{\tau}_1^\ast\tilde{\tau}_2. The branching fractions are less than 10% for H^0 -> h^0h^0 and 1% for A^0 -> h^0Z for m_A>400 GeV. The charged Higgs decays to neutralino plus chargino and sfermions with branching ratio as large as 40% and 60%, respectively. Moreover, the exclusion limit of leading MSSM Higgs search channel, namely gg,b\bar{b} -> H^0, A^0 -> tau^+ tau^-, is extrapolated to 14 TeV LHC with high luminosities. It turns out that the tau tau mode can essentially exclude regime with tan\beta>20 for L=300 fb^{-1} and tan\beta>15 for L=3000 fb^{-1}.Comment: 20 pages, 14 figure

    Revisiting simplified dark matter models in terms of AMS-02 and Fermi-LAT

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    We perform an analysis of the simplified dark matter models in the light of cosmic ray observables by AMS-02 and Fermi-LAT. We assume fermion, scalar or vector dark matter particle with a leptophobic spin-0 mediator that couples only to Standard Model quarks and dark matter via scalar and/or pseudo-scalar bilinear. The propagation and injection parameters of cosmic rays are determined by the observed fluxes of nuclei from AMS-02. We find that the AMS-02 observations are consistent with the dark matter framework within the uncertainties. The AMS-02 antiproton data prefer 30 (50) GeV - 5 TeV dark matter mass and require an effective annihilation cross section in the region of 4x10^{-27} (7x10^{-27}) - 4x10^{-24} cm^3/s for the simplified fermion (scalar and vector) dark matter models. The cross sections below 2x10^{-26} cm^3/s can evade the constraint from Fermi-LAT dwarf galaxies for about 100 GeV dark matter mass.Comment: 20 pages, 8 figures, 2 tables. arXiv admin note: text overlap with arXiv:1612.0950

    Type II Seesaw and tau lepton at the HL-LHC, HE-LHC and FCC-hh

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    The tau lepton plays important role in distinguishing neutrino mass patterns and determining the chirality nature in heavy scalar mediated neutrino mass models, in the light of the neutrino oscillation experiments and its polarization measurement. We investigate the lepton flavor signatures with tau lepton at LHC upgrades, i.e. HL-LHC, HE-LHC and FCC-hh, through leptonic processes from doubly charged Higgs in the Type II Seesaw. We find that for the channel with one tau lepton in final states, the accessible doubly charged Higgs mass at HL-LHC can reach 655 GeV and 695 GeV for the neutrino mass patterns of normal hierarchy (NH) and inverted hierarchy (IH) respectively, with the luminosity of 3000 fb1^{-1}. Higher masses, 975-1930 GeV for NH and 1035-2070 GeV for IH, can be achieved at HE-LHC and FCC-hh.Comment: 18 pages, 9 figures, 4 table

    Gradient Hard Thresholding Pursuit for Sparsity-Constrained Optimization

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    Hard Thresholding Pursuit (HTP) is an iterative greedy selection procedure for finding sparse solutions of underdetermined linear systems. This method has been shown to have strong theoretical guarantee and impressive numerical performance. In this paper, we generalize HTP from compressive sensing to a generic problem setup of sparsity-constrained convex optimization. The proposed algorithm iterates between a standard gradient descent step and a hard thresholding step with or without debiasing. We prove that our method enjoys the strong guarantees analogous to HTP in terms of rate of convergence and parameter estimation accuracy. Numerical evidences show that our method is superior to the state-of-the-art greedy selection methods in sparse logistic regression and sparse precision matrix estimation tasks

    Simulation based selection of competing structural econometric models

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    This paper proposes a formal model selection test for choosing between two competing structural econometric models. The procedure is based on a novel lack-of-fit criterion, namely, the simulated mean squared error of predictions (SMSEP), taking into account the complexity of structural econometric models. It is asymptotically valid for any fixed number of simulations, and allows for any estimator which has a vn asymptotic normality or is superconsistent with a rate at n. The test is bi-directional and applicable to non-nested models which are both possibly misspecified. The asymptotic distribution of the test statistic is derived. The proposed test is general regardless of whether the optimization criteria for estimation of competing models are the same as the SMSEP criterion used for model selection. An empirical application using timber auction data from Oregon is used to illustrate the usefulness and generality of the proposed testing procedure.Lack-of-fit, Model selection tests, Non-nested models, Simulated mean squared error of predictions